1. Field of the Invention
The present invention relates to a semiconductor device having a circuit constituted by a thin film transistor (hereinafter, referred to as TFT) and a method of fabricating thereof. For example, the invention relates to an electro-optic device represented by a liquid crystal panel and an electronic device mounted with such an electro-optic device as a part.
Further, in the specification, a semiconductor device generally indicates a device capable of functioning by utilizing semiconductor properties and all of electro-optic devices, semiconductor circuits and electronic device are defined as semiconductor devices.
2. Description of the Related Art
In recent years, attention is attracted to a technology of constituting a thin film transistor (TFT) by using a semiconductor thin film (thickness: about several through several hundreds nm) formed above a substrate having an insulating surface. The thin film transistor is widely applied to an electronic device such as IC or an electro-optic device and development thereof is expedited particularly as a switching element of an image display device.
In a liquid crystal display device, attention is attracted to an active matrix type liquid crystal display device arranging pixel electrodes in matrix and using TFTs as switching elements connected to the respective pixel electrodes to provide high grade image.
According to the active matrix type liquid crystal display device, there are known two kinds of types of a transmission type and a reflection type by gross classification.
Particularly, according to the reflection type liquid crystal display device, in comparison with the transmission type liquid crystal display device, there is provided an advantage of small power consumption since a backlight is not used and there is increased demand therefore as a directly viewing type display for a mobile computer or a video camera.
Further, the reflection type liquid crystal display device displays brightness and darkness by selecting a state in which incident light is reflected by a pixel electrode and is outputted to outside of the device and a state in which incident light is not outputted to outside the device by utilizing an optical modulating operation of liquid crystal and displays an image by a combination of these. Generally, the pixel electrode in the reflection type liquid crystal display device comprises a metal material having high optical reflectance such as aluminum and is electrically connected to a switching element of a thin film transistor (hereinafter, referred to as TFT).
Further, according to a liquid crystal display device, a liquid crystal material is sandwiched between an element substrate arranged with TFTs constituting semiconductors by amorphous silicon or polysilicon in matrix and respectively formed with pixel electrodes connected to respective TFTs and source lines and gate lines, and an opposed substrate having opposed electrodes arranged to be opposed thereto. Further, a color filter for color display is pasted to the opposed substrate. Further, the element substrate and the opposed substrate are respectively arranged with polarizers as optical shutters for displaying color image.
According to the reflection type liquid crystal display device, conventionally, after forming the pixel electrode, a surface thereof is made to be recessed and projected by adding a step of a sand blast process or an etching process to thereby prevent mirror face reflection and a whiteness degree is increased by scattering reflected light.
According to the invention, there are formed projected and recessed portions for preventing mirror face reflection of a reflecting electrode.
According to the present invention, a method of fabricating a liquid crystal display device of a reflection type is characterized in that a projected portion is formed by using the same photomask as that in forming TFT to achieve light scattering performance by providing recessed and projected portions on a surface of a pixel electrode. Further, the projected portion is pertinently provided on a substrate at a pixel region other than wirings and a TFT portion. Further, projected and recessed portions are formed on a surface of a pixel electrode along projected and recessed portions formed at a surface of an insulating film covering the projected portion.
According to an aspect of the invention disclosed in the specification, there is provided a semiconductor device comprising TFT including a semiconductor layer on an insulating surface, an insulating film on the semiconductor layer and a gate electrode on the insulating film, a plurality of projected portions on the insulating surface, an interlayer insulating film covering the TFT and the projected portions and having a projected and recessed surface, and a pixel electrode electrically connected to the TFT and having a projected and recessed surface on the interlayer insulating film.
Further, it should be noted that an insulating film covering a gate electrode of a thin film transistor is formed, and a pixel electrode in contact with a projected portion not overlapped with the insulating film may be formed. Thus, according to another aspect of the invention, there is provided a semiconductor device comprising TFT including a semiconductor layer on an insulating surface, an insulating film on the semiconductor layer and a gate electrode on the insulating film, a plurality of projected portions on the insulating surface, and a pixel electrode brought into contact with the projected portions, having a projected and recessed surface and electrically connected to the TFT.
According to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the projected portion is a laminated object of a material layer formed by the same material as that of the semiconductor layer of the TFT, a material layer formed by the same material as a material of the insulating film of the TFT and a material layer formed by the same material as that of the gate electrode of the TFT.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the projected portion is a laminated object of a material layer formed by the same material as that of the insulating film of the TFT and a material layer formed by the same material as that of the gate electrode of the TFT.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the projected portion is a material layer formed by the same material as that of the gate electrode of the TFT.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the plurality of projected portions include projected portions having at least different heights.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the plurality of projected portions include projected portions having at least different structures.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the semiconductor device is a liquid crystal display device of a reflection type in which the pixel electrode comprises a film having a major component of Al or Ag or a laminated film of these.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects, further comprising a first light shielding portion comprising laminated layers of a first color layer and a second color layer, and a second light shielding portion comprising laminated layers of the first color layer and a third color layer, wherein the first light shielding portion and the second light shielding portion are formed to overlap an interval between an arbitrary one of the pixel electrode and the pixel electrode contiguous to the arbitrary one of the pixel electrode.
Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein an amount of reflected light of the first light shielding portion and an amount of reflected light of the second light shielding portion are different from each other. Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the first color layer is constituted by red color. Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the second color layer is constituted by blue color. Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the third color layer is constituted by green color. Further, according to another aspect of the invention, there is provided the semiconductor device according to the above-described respective aspects wherein the first light shielding portion and the second light shielding portion are provided at an opposed substrate.
Further, in order to realize the above-described structure, according to another aspect of the invention, there is provided a method of fabricating a semiconductor device comprising a step of forming a semiconductor layer on an insulating surface, a step of forming a first insulating film on the semiconductor layer, a step of forming a conductive layer overlapping the semiconductor layer on the first insulating film and forming a projected portion comprising a laminated structure of the semiconductor layer and the first insulating film and the conductive layer, a step of forming a second insulating film covering the projected portion, and a step of forming a pixel electrode on the second insulating film, wherein the pixel electrode overlaps the projected portion and includes projected and recessed portions on a surface thereof. It should be noted that the projected portion corresponds to numeral 900 in FIG. 20.
Further, in order to realize the above-described structure, according to another aspect of the invention, there is provided a method of fabricating a semiconductor device comprising a step of forming a first insulating film on an insulating surface, a step of forming a conductive layer on the first insulating film and forming a projected portion comprising a laminated structure of the first insulating film and the conductive layer, a step of forming a second insulating film covering the projected portion, and a step of forming a pixel electrode on the second insulating film, wherein the pixel electrode overlaps the projected portion and includes projected and recessed portions on a surface thereof. It should be noted that the projected portion corresponds to numeral 901 in FIG. 20, and the first insulating film constituting the projected portion has the same shape as the conductive layer when viewed from upper side.
Further, in order to realize the above-described structure, according to another aspect of the invention, there is provided a method of fabricating a semiconductor device comprising a step of forming a conductive layer on an insulating surface and forming a projected portion comprising the conductive layer, a step of forming an insulating film covering the projected portion, and a step of forming a pixel electrode on the insulating film, wherein the pixel electrode overlaps the projected portion and includes projected and recessed portions on a surface thereof.
Further, according to another aspect of the invention, there is provided the method of fabricating a semiconductor device according to the above-described aspects wherein the semiconductor device is a liquid crystal display device of a reflection type in which the pixel electrode comprises a film having a major component of Al or Ag or a laminated film of these.
Further, according to another aspect of the invention, there is provided the method of fabricating a semiconductor device according to the above-described aspects wherein TFT is formed by the same step as that of forming the projected portion.
Further, according to another aspect of the invention, there is provided the method of fabricating a semiconductor device according to the above-described aspects wherein the pixel electrode is connected to TFT formed by the same step as that of forming the projected portion.